2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 - - 20, 2006 20, 2006 1 1 Introduction to the New ASD/LRFD Introduction to the New ASD/LRFD Unified Specifications for the Design Unified Specifications for the Design of K of K - - Series Joists, LH Series Joists, LH - - and DLH and DLH - - Series Joists and Joist Girders Series Joists and Joist Girders Perry S. Green, PhD, SJI Technical Director Timothy J. Holtermann, PE, SE SJI Engineering Practice Committee Chair and Corporate Engineering Manager, Canam Steel Corporation
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2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 11
Introduction to the New ASD/LRFD Introduction to the New ASD/LRFD Unified Specifications for the Design Unified Specifications for the Design
of Kof K--Series Joists, LHSeries Joists, LH-- and DLHand DLH--Series Joists and Joist GirdersSeries Joists and Joist Girders
Perry S. Green, PhD, SJI Technical Director
Timothy J. Holtermann, PE, SESJI Engineering Practice Committee Chair and
TensionCompressionBendingSimilarities and Differences with the 2005 AISC Specification for Structural Steel Buildings
• 2005 Code of Standard PracticeThe 2006 International Building CodePractical Usage – A Design Example
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 33
Background and DevelopmentBackground and Development
The Steel Joist Institute was founded in 1928 and produced it’s first Catalog and Specifications in 1932.
The 2005 Catalog is the 42nd Edition, the last being published in 2002.
The K-Series, LH- and DLH-Series and Joist Girder Specifications are ANSI accredited and have already been approved by the ICC for the 2006 International Building Code.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 44
Background and DevelopmentBackground and Development
The Steel Joist Institute developed, but never published, an LRFD Specification.After learning that AISC planned a dual specification for both ASD and LRFD, SJI decided that it would be appropriate to do the same for joists.The goal is to make the use of joists convenient for the Specifying Professional who is using either design method.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 55
2005 SJI 422005 SJI 42ndnd Edition CatalogEdition CatalogSteel Joist Institute
Accessories and Details K-Series Standard Specifications
• K-Series Load Tables• KCS Joists
LH- and DLH-Series Standard Specifications• LH- and DLH-Series Load Tables
Joist Girders Standard Specifications• Joist Girder Weight Tables
Referenced Specifications, Codes and StandardsCode of Standard Practice for Steel Joists and Joist GirdersGlossaryAppendices
A) Joist Substitutes, K-SeriesB) TCXs and Extended Ends, K-SeriesC) Economy Tables, K-SeriesD) Fire-Resistance Ratings with Steel JoistsE) OSHA Safety Standards for Steel Erection
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 66
Accessories and Details:Accessories and Details:Added MembersAdded Members
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 77
Accessories and Details: KAccessories and Details: K--Series Series Joists Selected Bridging DetailsJoists Selected Bridging Details
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 88
Accessories and Details: LHAccessories and Details: LH-- and DLHand DLH--Series Joists Selected Bridging DetailsSeries Joists Selected Bridging Details
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 99
Accessories and Details: LHAccessories and Details: LH-- and DLHand DLH--Series Joists Selected Bridging DetailsSeries Joists Selected Bridging Details
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1010
Accessories and Details: Accessories and Details: KK--Series Joists Sloped SeatsSeries Joists Sloped Seats
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1111
Accessories and Details:Accessories and Details:LHLH-- and DLHand DLH--Series Sloped SeatsSeries Sloped Seats
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1212
Accessories and Details:Accessories and Details:Approximate Duct Opening SizesApproximate Duct Opening Sizes
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1313
Joist GirdersJoist Girders
2002 SJI Joist Girder Specification limitations on standard product:
1. Maximum span = 60 feet2. Maximum depth = 72 inches3. Maximum panel point load = 20 kips
Allowable Strength Design (ASD)
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1414
Joist GirdersJoist Girders
2005 SJI Joist Girder Specification limitations on standard product:
1. Maximum span = 120 feet2. Maximum depth = 120 inches3. Maximum panel point load = 56 kips
Allowable Strength Design (ASD)Maximum panel point load = 84 kips
Load and Resistance Factor Design (LRFD)
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1515
Joist GirdersJoist Girders
Joist Girder Weight Tables• Maximum chord angle size is 6 x 6 x ¾
Applicable to all joist manufacturers• Some joist manufacturers will be able to go
up to a 8 x 8 chord angle, but that will be a non-standard SJI product
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1616
Joist GirdersJoist Girders
Joist Girder Weight Tables• The weight table can not cover every
combination of span, panel spacing and kip loading
• A Joist Girder can be made to fit within any of the “gaps” in the weight table
• Remember that the weight table is provided as a design aid for the structural engineer to help provide an approximate value for the Joist Girder self weight
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1717
New, unified specifications for the K-Series, LH- and DLH-Series and Joist Girders similar to AISC and AISI allowing an ASD orLRFD approach to joist design have been developed.
The end product for the Specifying Professional or structural engineer remains the same; there will be no noticeable changes in the appearance of a fabricated joist and there are no new series or designations.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1818
The equations for computing compression, tension, and bending capacity closely follow the new AISC equations.In keeping with SJI history, the specification is written in terms of “stresses” rather than “forces”.The combined interaction equations more closely resemble previous SJI Specifications than AISC, but have been modified with a primary goal of consistent results between ASD and LRFD.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 1919
Using the New Unified Specifications• Contract drawings need to clearly show if the
project is ASD or LRFD• For special loads, contract drawings need to
define any load combinations if other than those given in ASCE 7
• An ASD or LRFD joist or Joist Girder of the same designation will be identical, but the choice of ASD or LRFD may affect which designation is selected
• LRFD projects will need to show all design loads as already factored
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2121
Load CombinationsLoad Combinations
Only two basic load combinations are given:LRFD 1.4D
1.2D + 1.6 (L, or Lr, or S, or R)ASD D
D + (L, or Lr, or S, or R)When special loads are specified and the Specifying Professional does not provide the load combinations, the provisions of ASCE 7 Minimum Design Loads for Buildings and Other Structures shall be used for LRFD and ASD load combinations.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2222
Design and Allowable StressesDesign and Allowable Stresses
The following LRFD Resistance Factors ( φ ) and ASD Safety Factors ( Ω ) are defined for determining tension, compression and bending stresses:
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2323
Design and Allowable StressesDesign and Allowable Stresses
Section 4.2(a) Tension
For Chords: Fy = 50 ksi (345 MPa)
For Webs: Fy = 50 ksi (345 MPa) or Fy = 36 ksi (250 MPa)
Design Stress = 0.9Fy (LRFD) (4.2-1)
Allowable Stress = 0.6Fy (ASD) (4.2-2)
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2424
Design and Allowable StressesDesign and Allowable StressesSection 4.2(b) CompressionFor members with
(4.2-3)
For members with
Fcr = 0.877Fe (4.2-4)
Where Fe = Elastic buckling stress determined in accordance with Equation 4.2-5
yQFE71.4r ≤l
yF
QF
cr F658.0QF ey
⎥⎥⎦
⎤
⎢⎢⎣
⎡=
⎟⎠⎞
⎜⎝⎛
yQFE4.71r >l
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2525
Design and Allowable StressesDesign and Allowable StressesSection 4.2(b) Compression (cont’d)
(4.2-5)
Where l is the panel length, in inches (mm), as defined in Section 4.2(b) and rx is the radius of gyration about the axis of bending.For hot-rolled sections, “Q” is the full reduction factor for slender compression elements.
Design Stress =0.9Fcr (LRFD) (4.2-6)
Allowable Stress =0.6Fcr (ASD) (4.2-7)
( )2
2
e
r
EFl
π=
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2626
Design and Allowable StressesDesign and Allowable StressesSection 4.2(b) Compression (cont’d)In the above equations, l is taken as the distance in inches (millimeters) between panel points for the chord members and the appropriate length for web members, and r is the corresponding least radius of gyration of the member or any component thereof. E is equal to 29,000 ksi (200,000 MPa).
Use 1.2 l / rx for a crimped, first primary compression web member when a moment-resistant weld group is not used for this member; where rx = member radius of gyration in the plane of the joist.
For cold-formed sections the method of calculating the nominal column strength is given in the AISI, North American Specification for the Design of Cold-Formed Steel Structural Members.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2727
Design and Allowable StressesDesign and Allowable Stresses
Section 4.2(b) Compression (cont’d)
2005 AISC SpecificationE7. MEMBERS WITH SLENDER ELEMENTS
For cross section composed of only unstiffenedslender elements, Q = Qs (Qa = 1.0). For cross sections composed of only stiffened slender elements, Q = Qa (Qs = 1.0). For cross sections composed of both stiffened and unstiffened slender elements, Q = QsQa.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2828
)127E(FE91
tbwhen
tbF
E53.0Q
)117E(FE91.0
tb
FE45.0when
EF
tb76.034.1Q
)107E(FE45.0
tbwhen0.1Q
y2
y
s
yy
ys
ys
−≥
⎟⎠⎞
⎜⎝⎛
=
−<<⎟⎠⎞
⎜⎝⎛−=
−≤=
E7-1(c) For single angles:
Slender Slender UnstiffenedUnstiffened Elements QElements QssTable B4.1 Limiting Width-Thickness Ratios for Compression Elements Unstiffened Elements
Case 5: Uniform compression in legs of single angles, legs of double angles with separators, and all other unstiffened elements
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 2929
Design and Allowable StressesDesign and Allowable StressesThe allowable compression stress is given by the following formulas in AISC-ASD 9th Edition
( )
( ) ( ))12E(
C8rKl
C8rKl3
35
FC2
rKl1F
3c
3
c
y2c
2
a −−+
⎥⎦
⎤⎢⎣
⎡−
=
( ))22E(
rKl23E12F 2
2
a −π
=
y
2
c FE2Cwhere π
=
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3030
Design and Allowable StressesDesign and Allowable Stresses
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3131
Design and Allowable StressesDesign and Allowable Stresses
Section 4.2(c) BendingBending calculations are to be based on using the elastic section modulus.For chords and web members other than solid rounds:
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3333
Design and Allowable StressesDesign and Allowable Stresses
Section 4.4 The combined interaction equations have been modified to take advantage of the “8/9”factor now allowed by AISC on the bending part of the interaction.The constants in the “moment magnification”parts of the equations were carefully constructed to produce the same interaction result for equal ASD or LRFD Required Stresses.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3434
Design and Allowable StressesDesign and Allowable Stresses
Section 4.4 MembersWhen the panel length exceeds 24 inches, the top chord shall be designed as a continuous member subject to combined axial and bending stresses and shall be so proportioned that:
For LRFD:At the panel point:
(4.4-1)ybuau F9.0ff ≤+
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3535
Design and Allowable StressesDesign and Allowable Stresses
For LRFD:At the mid panel:
For,(4.4-2)
For,(4.4-3)
2.0F
f
crc
au ≥φ
0.1FQ
Ff
1
fC98
Ff
ybec
au
bum
crc
au ≤
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
φ⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛φ
−
+φ
2.0F
f
crc
au <φ
0.1FQ
Ff
1
fCF2
f
ybec
au
bum
crc
au ≤
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
φ⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛φ
−
+⎟⎟⎠
⎞⎜⎜⎝
⎛φ
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3636
Design and Allowable StressesDesign and Allowable StressesWhere:Fau = Pu/A = Required compressive stress, ksi (MPa)P = Required axial strength using LRFD load
combinations, kips (N)Fbu = Mu/S = Required bending stress at the location under
consideration, ksi (MPa)Mu = Required flexural strength using LRFD load
combinations, kip-in. (N-mm)S = Elastic Section Modulus, in.3 (mm3)Fcr = Nominal axial compressive stress in ksi (MPa) based on
l/r as defined in Section 4.2(b)Cm = 1 - 0.3 fau/φFe for end panelsCm = 1 - 0.4 fau/φFe for interior panelsFy = Specified minimum yield strength, ksi (MPa)Q = Form factor defined in Section 4.2(b)A = Area of the top chord, in.2 (mm2)
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3737
Design and Allowable StressesDesign and Allowable Stresses
Section 4.4 Members (cont’d)For ASD:
At the panel point:
(4.4-4)yba F6.0ff ≤+
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3838
Design and Allowable StressesDesign and Allowable Stresses
For ASD:At the mid panel:
For,(4.4-5)
For,(4.4-6)
2.0Ff
a
a ≥ 1.0QF
F1.67f
1
fC98
Ff
be
a
bm
a
a ≤
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−
+
2.0Ff
a
a < 1.0QF
F1.67f
1
fC2Ff
be
a
bm
a
a ≤
⎥⎥⎥⎥⎥
⎦
⎤
⎢⎢⎢⎢⎢
⎣
⎡
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−
+⎟⎟⎠
⎞⎜⎜⎝
⎛
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 3939
Design and Allowable StressesDesign and Allowable Stresses
kips (N)fb = M/S = Required bending stress at the location under
consideration, ksi (MPa)M = Required flexural strength using ASD load
combinations, k-in. (N-mm)S = Elastic Section Modulus, in.3 (mm3)Fa = Allowable axial compressive stress based on l/r as
defined in Section 4.2(b), ksi (MPa)Fb = Allowable bending stress; 0.6Fy, ksi (MPa)Cm = 1 - 0.50 fa/Fe for end panelsCm = 1 - 0.67 fa/Fe for interior panels
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4040
Design and Allowable StressesDesign and Allowable Stresses
Within a discontinuous panel point, the effects of combined shear and axial stress are considered.
For double angle chord members, only the area of the vertical legs is used in computing the shear stress.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4141
Design and Allowable StressesDesign and Allowable Stresses
Node shear:
For LRFD:
For ASD:
)1SJI(F6.0)f(4)f(2/1 y2
v2
t −≤+
)2SJI(F4.0)f(4)f(2/1 y2
v2
t −≤+
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4242
Design and Allowable StressesDesign and Allowable Stresses
For Joist Girders, a check is made for bearing capacity of the outstanding leg of a double angle top chord in combination with axial compression.
The allowable bearing end reaction (Pp) at each chord angle is computed and compared against ½ the girder panel point load.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4343
Design and Allowable StressesDesign and Allowable Stresses
Allowable reaction is lesser of:
For LRFD: and
For ASD: and
[ ] )3SJI()Kb(66.5g)Kb(2
FtP y
2
p −−+−
=
pP9.0 )4SJI(QF9.0f6.1P9.0
y
ap −
⎥⎥⎦
⎤
⎢⎢⎣
⎡−
)5SJI(QF6.0f6.1P6.0
y
ap −
⎥⎥⎦
⎤
⎢⎢⎣
⎡−pP6.0
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4444
Design and Allowable StressesDesign and Allowable Stresses
An allowance is made for eccentricity at the supports by limiting the top chord end panel and the end web member to 90 percent of the Design Stress or Allowed Stress.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4545
Code of Standard Practice HighlightsCode of Standard Practice Highlights
Document renamed, Recommendedremoved from titleThree sections revised; modified and edited
• Section 2. Joists and Accessories• Section 5. Estimating• Section 6. Plans and Specifications
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4646
Plans and SpecificationsPlans and SpecificationsPlans Furnished by BuyerThe Buyer shall furnish the Seller plans and specifications as prepared by the Specifying Professional showing all material requirements and steel joist and/or steel joist girder designations, the layout of walls, columns, beams, girders and other supports, as well as floor and roof openings and partitions correctly dimensioned. The live loads to be used, the wind uplift if any, the weights of partitions and the location and amount of any special loads, such as monorails, fans, blowers, tanks, etc., shall be indicated. The elevation of finished floors, roofs, and bearings shall be shown with due consideration taken for the effects of dead load deflections.
(a) Loads(b) Connections(c) Special Considerations
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4747
LoadsLoads• The Steel Joist Institute does not presume to establish the
loading requirements for which structures are designed.
• The Steel Joist Institute Load Tables are based on uniform loading conditions and are valid for use in selecting joist sizes for gravity loads that can be expressed in terms of "pounds per linear foot" (kiloNewtons per Meter) of joist. The Steel Joist Institute Joist Girder Weight Tables are based on uniformly spaced panel point loading conditions and are valid for use in selecting Joist Girder sizes for gravity conditions that can be expressed in kips (kiloNewtons) per panel point on the Joist Girder.
• The Specifying Professional shall provide the nominal loads and load combinations as stipulated by the applicable code under which the structure is designed and shall provide the design basis (ASD or LRFD).
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4848
LoadsLoads• The Specifying Professional shall calculate and provide the
magnitude and location of ALL JOIST and JOIST GIRDER LOADS. This includes all special loads (drift loads, mechanical units, net uplift, axial loads, moments, structural bracing loads, or other applied loads) which are to be incorporated into the joist or Joist Girder design. For Joist Girders, reactions from supported members shall be clearly denoted as point loads on the Joist Girder. When necessary to clearly convey the information, a Load Diagram or Load Schedule shall be provided.
• The Specifying Professional shall give due consideration to:1. Ponded rain water2. Accumulation of snow3. Wind forces4. Seismic forces
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 4949
LoadsLoads
Where the LRFD method is being used, the joist manufacturer should be provided with total design loads on the contract drawings that are already factored.This is important since the proportions of dead and live load are not always given (For example, a Joist Girder designation).
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5050
LoadsLoads
Replace the “K” at the end of Joist Girder designations with “F” to denote factored loads.
48G10N12K for ASD48G10N18F for LRFD
For wind uplift, the NET uplift is requested; i.e., the result of the appropriate load combination involving “D” and “W”.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5151
Concentrated LoadsConcentrated LoadsWhere concentrated loads occur, the magnitude and location of these concentrated loads shall be shown on the structural drawings when, in the opinion of the Specifying Professional, they may require consideration by the joist manufacturer.The Specifying Professional shall use one of the following options that allows the:
- Estimator to price the joists.- Joist manufacturer to design the joists properly.- Owner to obtain the most economical joists.
OPTION 1: Select a Standard SJI joist for the UDL and provide the load and location of any additional loads.
OPTION 2: Select a KCS joist using moment and end reaction.OPTION 3: Specify a SPECIAL joist with load diagrams.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5252
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5353
Concentrated LoadsConcentrated LoadsASD Load Diagram per ASCE 7 2.4.1 (3): D + S
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5454
Concentrated LoadsConcentrated LoadsThe load combinations previously shown are for the referenced examples only.It is not to be presumed that the joist designer is responsible for the applicable building code load combinations.If the loading criteria are too complex to adequately communicate in a simple load diagram, then the specifying professional shall provide a load schedule showing the specified design loads, load categories, and required load combinations with applicable load factors (i.e. for ASD or LRFD).
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5555
2003 International Building Code2003 International Building Code
2206.1 General. The design, manufacturing and use of open web steel joists and joist girders shall be in accordance with one of the following SJI specifications:
1. Standard Specifications for Open Web Steel Joists, K Series
2. Standard Specifications for Longspan Steel Joists, LH Series and Deep Longspan Steel Joists, DLH Series
3. Standard Specifications for Joist Girders
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5656
2006 International Building Code2006 International Building Code
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5757
2006 International Building Code2006 International Building Code
IBC Code Revision BackgroundCompromise between SJI and NCSEA
An agreement was worked out between the two parties and IBC that initiated with a concern that steel joist details could fall outside the direct supervision of either the EOR or Specialty Engineer
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5858
2006 International Building Code2006 International Building Code
2206.2 Design.
This section outlines the responsibility of the Registered Design Professional and what needs to be shown on the contract drawings.
1. Special loads2. Special considerations3. Deflection criteria for non-SJI standard joists
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 5959
2006 International Building Code2006 International Building Code
2206.3 Calculations.
This section describes that the RDP may request sealed calculations from the joist manufacturer’s registered design professional. In addition to the standard calculation package(s) the following shall be included:
1. Non-SJI standard bridging details2. Connection details for: Non-SJI standard
connections; field splices; and joist headers
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 6060
2006 International Building Code2006 International Building Code
2206.4 Steel Joist Drawings.
This section shows the products as specified in the contract drawings.
These drawings will not be sealed.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 6161
2006 International Building Code2006 International Building Code
2206.4 Steel Joist Drawings.
Joist Placement Plans1. Listing of all applicable loads2. Profiles for non-standard joist and joist girder
configurations3. Connection requirements4. Deflection criteria for non-SJI standard joists5. Size, location and connections for all bridging6. Joist headers
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2006 International Building Code2006 International Building Code
2206.5 Certification.
The joist manufacturer shall issue a Certificate of Compliance to the SJI Specifications and contract documents at the completion of fabrication.
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Practical Usage Practical Usage –– A Design ExampleA Design Example
The joist manufacturer needs to know:
• Is the structural design, and therefore the joist design, ASD or LRFD?
• What is the applicable model building code?
• Are there special loads that require load combinations other than those of ASCE 7?
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Overall Building LayoutOverall Building Layout
A
B
C
D
16(5) SPACES @ 40’-0” = 200’-0”
EAVE HEIGHT = 30’-0”
108’-
0”
NORTH
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Design Example using ASD and LRFDDesign Example using ASD and LRFD
Consider a typical interior bay of a building with the following design parameters:
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 6666
Design Example using ASD and LRFDDesign Example using ASD and LRFD
Required Loads or Load Combinations to be Provided from the Engineer of Record Include:
Dead Load, Live Load, Rain Load, Snow Load, Wind Load, Seismic Load, Other Loads, etc.
These Loads can be Uniformly Distributed Loads, Other Types of Distributed Loads or Concentrated Loads, and depending on the Design Methodology selected, need to be either unfactored or factored.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 6767
Self Weight of Joists and Joist GirdersSelf Weight of Joists and Joist Girders
When specifying joists, always include the self weight of joists and bridging.
When specifying joist girders, it is normal that the self weight of the girders is included in the specified loads. When this is not the case, the design drawings must clearly note that self weight is not included and the manufacturer must add self weight.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 6868
Design Example using ASD and LRFDDesign Example using ASD and LRFD
Design Parameters for St. Louis, MO
Building Eave Height, h = 30 ft.Building Importance Factor, I = 1.0Basic Wind Speed, V = 90 mphBuilding Exposure Category B, Kzt = 1.0Roof Slope = 1/4 : 12 (low slope)
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 6969
Snow LoadsSnow Loads
Note: Unbalanced loads need not be considered for θ> 70° or for θ < larger of 2.38° and 70/W + 0.5
W
Balanced
Unbalanced W ≤ 20 ft.
Unbalanced W > 20 ft.
ps
I * pg
0.3ps ps
hd γ/√S8/3 * hd/√S
S
1
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7070
Snow Load MapSnow Load Map
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Wind Load MapWind Load Map
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7272
Design Example using ASD and LRFDDesign Example using ASD and LRFDDesign Dead Load = 22 psf
Roof Live Load Lr = 20 psfSnow Load pg = 20 psf; ps = 20 psf
Per ASCE 7-05, Section 7.10 add 5 psf rain-on-snow surcharge,
Design Snow Load = 20 psf + 5 psf = 25 psf
Per ASCE 7-05, Figure 6.3 Components and Cladding, Zone 1 (Interior Bay), Effective Wind Area > 100 sf, Net Design Wind Pressure,
pnet30 = 4.7 psf, -13.3 psf
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7373
Wind Loads: UpliftWind Loads: Uplift
When wind uplift is a design consideration, it should be specified as net uplift on the joists and Joist Girders.
The Engineer of Record knows the design dead load and if there are collateral dead loads that should not be deducted from the gross uplift.
Joists are considered components and cladding.
The joist tributary width need not be less than one-third the joist span.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7474
Wind Loads: UpliftWind Loads: Uplift
Joist Girders can be considered part of the main wind force-resisting system, although it is common to simply apply the joist uplift end reactions.
Joist Girder tension webs must be designed to resist , in compression, 25 percent of their axial force.
Hence, uplift loads on a Joist Girder of less than 25 percent of the gravity loads have minimal or no effect on the girder design.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7575
Design Example using ASD and LRFDDesign Example using ASD and LRFD
Other Design Considerations
The interior bay has a hanging catwalk that is attached to the bottom chords of two joists at three panel point locations (600 lbs each, unfactored).
One joist of the interior bay has a 15K top chord axial load due to seismic.
No Live Load Reduction has been taken.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7676
Basic Load CombinationsBasic Load Combinations
Basic load combinations. Where strength or load and resistance factor design is used, structures and portions thereof shall resist the most critical effects resulting from the following combinations of factored loads:
IBC 1605.2.1 Load and Resistance Factor Design
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Basic Load CombinationsBasic Load Combinations
1.4D (Eqn 16-1)1.2D + 1.6L + 0.5(Lr or S or R) (Eqn 16-2)1.2D + 1.6(Lr or S or R) + (f1L or 0.8W) (Eqn 16-3)1.2D + 1.6W + f1L + 0.5(Lr or S or R) (Eqn 16-4)1.2D + 1.0E + f1L + f2S (Eqn 16-5)0.9D + 1.6W (Eqn 16-6)0.9D + 1.0E (Eqn 16-7)
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 7878
Basic Load CombinationsBasic Load Combinationsf1 = 1.0 for floors in places of public assembly, for
live loads in excess of 100 psf and for parking garage live load, and
= 0.5 for other live loadsf2 = 0.7 for roof configurations (such as saw tooth)
that do not shed snow off the structure, and
= 0.2 for other roof configurations
Exception: Where other factored load combinations are specifically required by the provisions of this code, such combinations shall take precedence.
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Basic Load CombinationsBasic Load Combinations
Basic load combinations. Where allowable stress design (working stress design), as permitted by this code, is used, structures and portions thereof shall resist the most critical effects resulting from the following combinations of loads:
IBC 1605.3.1 Allowable Stress Design
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Basic Load CombinationsBasic Load Combinations
D (Eqn 16-8)D + L (Eqn 16-9)D + (Lr or S or R) (Eqn 16-10)D + 0.75L + 0.75(Lr or S or R) (Eqn 16-11)D + (W or 0.7E) (Eqn 16-12)D + 0.75((W or 0.7E) + L + (Lr or S or R)) (Eqn 16-13)0.6D + W (Eqn 16-14)0.6D + 0.7E (Eqn 16-15)
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Basic Load CombinationsBasic Load Combinations
Exceptions: 1. Crane hook loads need not be combined with
roof live load or with more than three-fourths of the snow load or one-half of the wind load.
2. Flat roof snow loads of 30 psf or less need not be combined with seismic loads. Where flat roof snow loads exceed 30 psf, 20 percent shall be combined with seismic loads.
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IBC 1605.3.1.1 Stress increases.
Basic Load CombinationsBasic Load Combinations
Increases in allowable stresses specified in the appropriate material chapter or the referenced standards shall not be used with the load combinations of Section 1605.3.1, except that a duration of load increase shall be permitted in accordance with Chapter 23 WOOD.
IBC 1605.3.1.2 Other loads.
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In lieu of the basic load combinations specified in Section 1605.3.1, structures and portions thereof shall be permitted to be designed for the most critical effects resulting from the following combinations. When using these alternate basic load combinations that include wind or seismic loads, allowable stresses are permitted to be increased or load combinations reduced, where permitted by the material section of this code or referenced standard. Where wind loads are calculated in accordance with Section 1609.6 or ASCE 7, the coefficient ω in the following formulas shall be taken as 1.3. For other wind loads ω shall be take as 1.0.
2006 Structures Congress St. Louis, MO May 18 2006 Structures Congress St. Louis, MO May 18 --20, 200620, 2006 8484
Specifying and Designing with Steel Joists and Joist Girders
Chelmsford, MA May 23, 2006Oakbrook, IL July 17, 2006St. Louis, MO September 19, 2006Salt Lake City, UT October 16, 2006Greensboro, NC November 15, 2006
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